Print inspecting method and apparatus

ABSTRACT

This invention relates to a technique for inspecting picture patterns on prints which are being run in a rotary press or the like, and more particularly to a method in which reference data read out of a reference print is written in a memory, and inspection data read out of a print under inspection is compared with the reference data for every picture element for instance to determine whether or not the print is acceptable, and an apparatus for practicing the method. The specific feature of the invention resides in that (1) in reading the above-described data a print running speed or the position of a picture pattern in the direction of width is detected to rewrite the reference data, (2) in data comparison, the comparison level is optionally set up, and (3) the data comparison is carried out not only for every picture element, but also for the sum of picture elements over the entire picture pattern and for the sum of picture elements arranged linearly in the print running direction.

DESCRIPTION

1. Technical Field

This invention relates to a method of accurately inspecting prints whichare being run in a rotary press or the like, in order to determinewhether or not the prints are acceptable, and to an apparatus forpracticing the method.

2. Background Art

In general, prints must be finished to a considerably high degree.Accordingly, an inspecting method sufficiently high in reliablity mustbe employed in inspecting such prints.

In a rotary press or the like, prints are being run at high speed.Accordingly, if a visual inspection method is employed, it is impossibleto inspect the prints in real time.

In order to overcome the difficulty, an inspecting method has beenproposed in which the picture pattern of a print being run is detectedby a one-dimensional image sensor camera or the like to provide videosignals, and the video signals thus provided, being handled as analogdata, are compared with the reference voltage to determine whether ornot the print is acceptable, or binary-coded with a predeterminedthreshold value thereby to determine the acceptability of the print.

The above-described method utilizing the analog video signals may detectdefects on a blank roll stock with high accuracy; however, it isdisadvantageous in that, in the case where the density varies widely asin the case of the picture pattern on a print, the accuracy fordetermining whether or not the print is acceptable is not sufficient.

In order to overcome this drawback, a method has been proposed in whichthe video signals are digitalized so that the video signals of theentire picture pattern of a print under inspection can be stored, videosignals obtained from a reference print are stored as reference data,and video signals obtained from a print under inspection are employed asinspection data, so that the inspection data is compared with thereference data which is read out for every picture element, to determinewhether or not the print is acceptable.

The method is much higher in inspection accuracy than the visualinspection method or the analog inspection method.

An object of this invention is to improve a conventional printinspection apparatus of digitalization type, thereby to provide a printinspecting apparatus in which the accuracy is much higher, an effectivemasking function is readily provided, and the operation is stable evenwhen the state of prints is changed.

DISCLOSURE OF THE INVENTION

The specific feature of the invention resides in that image data readout of a reference print is written in a memory while image data readout of a print under inspection is employed as inspection data, and whenthe inspection data is compared with the reference data, for instance,for every picture element to determine whether or not the print isacceptable, the reference data is rewritten by detecting not only theimage data but also the print running speed or the position of thepicture pattern in the direction of width.

The specific feature of the invention resides further in that, incomparing the detection data with the reference data for every pictureelement for instance, the comparison level is optionally set up forevery picture element.

The specific feature of the invention resides further in that the datacomparison is carred out not only for every picture element, but alsofor the sum of picture elements over the entire picture pattern and forthe sum of picture elements arranged linearly in the print runningdirection, and the results of comparison are generally judged todetermine whether or not the print is acceptable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing theoretically one example of aprint inspecting method according to a digitalization system.

FIG. 2 is an explanatory diagram outlining a reference data memory.

FIG. 3 is a block diagram showing the entire arrangement of one exampleof a print inspecting apparatus according to this invention.

FIG. 4 is a circuit diagram showing one example of a running postionsignal input circuit.

FIG. 5 is a time chart for a description of the operation.

FIG. 6 is a circuit diagram showing one example of a scanning directionsignal input circuit.

FIG. 7 is an explanatory diagram showing the relationships between theinspection surface of a printing cylinder and various signals.

FIG. 8 is an explanatory diagram showing the addresses on the inspectionsurface.

FIG. 9 is a circuit diagram showing one example of an address generatingcircuit.

FIG. 10 is an explanatory diagram showing examples of thecharacteristics which are required for an analog-to-digital converter.

FIG. 11 is a circuit diagram showing one example of a digital inputinterface.

FIG. 12 is a circuit diagram showing one example of an image emphasizingcircuit.

FIG. 13 is an explanatory diagram showing the arrangement of a datainput system and its signal in combination.

FIG. 14 is a circuit diagram showing one example of a common circuitarrangement.

FIG. 15 is an explanatory diagram showing a comparison and decisionoperation for every picture element.

FIG. 16 is a circuit diagram showing one example of a first featureextraction comparison decision circuit.

FIG. 17 is an explanatory diagram showing a comparison and decisionoperation by the sum of picture elements.

FIG. 18 is a circuit diagram showing one example of a second featureextraction comparison decision circuit.

FIG. 19 is an explanatory diagram showing a comparison and decisionoperation by the sum of picture elements in a particular direction.

FIG. 20 is a circuit diagram showing one example of a third featureextraction comparison decision circuit.

FIG. 21 is a circuit diagram showing one example of a general decisioncircuit.

FIG. 22 is an explanatory diagram showing picture patterns shifted on aprint.

FIG. 23 is an explanatory diagram showing the variations of pictureelement intensity due to the displacement of picture patterns.

FIG. 24 is an explanatory diagram showing the operation of a picturepattern position detector.

FIGS. 25 and 26 are explanatory diagrams showing position detectingmarks.

FIG. 27 is a circuit diagram showing one example of a reference datamemory rewrite signal generating circuit.

FIG. 28 is a flow chart for a description of the operation of thecircuit in FIG. 27.

FIG. 29 is an explanatory diagram showing the relationships between aprint running speed and an actual scanning direction.

FIG. 30 is an explanatory diagram showing variations in picture patternreading state which are due to variations in print running speed.

FIG. 31 is a flow chart showing one example of a reference data memoryrewriting operation according to running speed.

FIG. 32 is an explanatory diagram showing why masking is required ininspecting prints.

FIGS. 33 and 34 are characteristic diagrams for a description of therelationships between picture pattern density and optical intensity anddecision levels.

FIGS. 35 and 36 are explanatory diagrams showing effects of theinvention.

FIG. 37 is a diagram outlining a picture element control data memory.

FIG. 38 is a circuit diagram showing another example of the firstfeature extraction comparison decision circuit.

FIGS. 39 and 40 are explanatory diagrams showing examples of theoperation of setting data in the picture element control data memory.

The parts (A) and (B) of FIG. 41 are explanatory diagrams showing theconfiguration of a picture element in a detection area.

The parts (A) and (B) of FIG. 42 are explanatory diagrams showing thedifference in position shift detection sensitivity in two directions.

FIG. 43 is a flow chart showing one example of a data setting operation.

BEST MODE FOR CARRYING OUT THE INVENTION

Prior to this invention, a conventional digital type inspecting methodwill be described with reference to FIGS. 1 and 2, and thereafter oneembodiment of the invention will be described with reference to FIGS. 3through 43.

FIG. 1 shows the principle of one example of the conventional digitaltype inspecting method. In FIG. 1, reference character P designates aprint; CY, a printing cylinder; 1, an image sensor camera; 2, ananalog-to-digital (A/D) converter; SW, a change-over switch; M, areference data memory; and CO, a comparator.

The print P is a long sheet or film on which a predetermined picturepattern is repeatedly printed by a rotary press in the direction of runof the print. The print P is run by the printing cylinder CY.

The image sensor camera (hereinafter referred to an "IS camera", whenapplicable) 1 shoots the surface of the print 1 on which the picturepattern is printed; that is, the IS camera 1 scans one-dimensionally apredetermined portion thereof in a widthwise direction X perpendicularto the direction of run Y of the print paper, to provide a video signal.The one-dimensional video signal is digitalized by the A/D converter forevery number of picture elements, and is then applied to the change-overswitch.

The memory contents of the reference data memory M is as shown in FIG.2. That is, the reference data memory M is so designed that thedigitalized density data of picture elements can be written in and readout of addresses a which are arranged in the print width direction andin the print run direction. When the armature of the change-over switchSW is tripped as shown in FIG. 1 and the IS camera shoots apredetermined picture pattern portion of the print P, the density dataof the picture elements of a portion of the print in the direction ofwidth X are successively written in addresses arranged in the printwidth direction. This operation is repeatedly carred out as the print Pis run in the direction Y, so that the density data are written in theaddresses arranged in the direction of run. Finally, the image data, ina predetermined range, of the picture pattern on the print P are writtenin the reference data memory M.

When the armature of the change-over switch SW is tripped downwardly,image data successively read out of a predetermined range of the picturepattern on the print P are applied, as inspection data I to thecomparison circuit CO, and reference data S read out of the referencedata memory M for picture elements in correspondence thereto are appliedto the comparison circuit CO. The result of comparison is provided, asan output J, by the comparison circuit CO.

Accordingly, at a predetermined time instant immediately after theprinting operation has been started, the armature of the switch SW istripped to the reference data memory M after confirming that the print'spicture pattern is free from defects, so that image data obtained fromthe print P at that time are written in the reference data memory M.Thereafter, if the armature of the switch S is tripped over to thecomparison circuit CO, then the image data successively read out of theprint P are inputted, as the inspection data I, to the comparisoncircuit CO. Therefore, in the comparison circuit CO, the image data thusinputted are compared with the reference data S which are read out ofthe reference data memory M, successively for every picture element. Theresult of comparison is provided as the output J.

Thus, if the output J of the comparison circuit CO is detected so as todetect whether or not the reference data S coincides with the inspectiondata I, then it can be continuously determined whether or not the printP running at high speed is satisfactory during printing. This inspectionmethod is much higher in reliability than a visual inspection method.

FIG. 3 is a block diagram showing the entire arrangement of oneembodiment of the invention. In FIG. 3, a printing cylinder CY, an IScamera 1 and an A/D converter are similar to those in FIG. 1. Further inFIG. 3, reference numeral 3 designates a picture pattern positiondetector; 4, a picture pattern position signal input circuit; 5, arunning position signal input circuit; 6, a scanning direction signalinput circuit; 7, a digital input interface; 8, an address generatingcircuit; 9, a first feature extraction comparison decision circuit; 10,a second feature extraction comparison decision circuit; 11, a thirdfeature extraction comparison decision circuit; 12, a general decisioncircuit; 13, a reference data memory rewrite signal generating circuit;14, a reference data memory (corresponding to the memory M in FIG. 1);15, a picture element control data memory; 16, a buffer memory; 17, acomputer interface; 18, a monitoring address generating circuit; 19, amonitor interface; 20, a monitor; and 21, a computer, these circuitelements being connected through a bus.

As was described before, in such an inspecting system, it is necessarythat inspection data from a picture pattern repeatedly printed arecompared with the reference data for every picture element, andaccordingly it is essential to determine addresses definitelyrepresenting the picture surface of the picture pattern. For thispurpose, a rotary encoder RE is employed to detect the position inrotational direction of the printing cylinder CY which is necessary foraddressing, and the output signal of the rotary encoder RE is applied tothe running position signal input circuit 5, so that the latter 5provides signals representing the inspection starting point and theinspection ending point on the circumference of the printing cylinderCY.

One example of the running position signal input circuit 5 is as shownin FIG. 4. The rotary encoder RE outputs two kinds of signals; the firstone is a signal ZERO in the form of one pulse which is produced at apredetermined rotational position of the printing cylinder CY wheneverthe latter CY makes one revolution, and the second one is an A-phasesignal in the form of a predetermined number of pulses which areoutputted every revolution. Before the inspection is started, a setvalue is applied from the computer 21 through the computer interface 17to a latch circuit 22, where it is written, as a result of which asignal MEND representing the inspection ending point can be produced.

Similarly as in the above-described case, set values are written in thelatch circuits of the following circuits by means of the computer 21.

After being reset by the signal ZERO, the counter 24 counts the A-phasesignal. The output of the counter 24 is applied to a comparator 23,where it is compared with the set value of the latch circuit 22. Whenboth coincide with each other, the comparator 23 provides an output,which is supplied to a monostable multivibrator 26 (hereinafter referredto merely as "an MMV 26", when applicable) to trigger the latter 26, tocause the same 26 to provide the signal. Thus, the inspection endingpoint has been set up. On the other hand, the inspection starting pointis represented by the signal ZERO, which, in this case, is referred toas "a signal MZERO". Thus, the inspection period is between theoccurrences of the signals MZERO and MEND. The A-phase signal of therotary encoder RE is supplied to the bus as it is, so as to be employedas a clock signal in other circuits, thus being referred to as "a signalMCLK" in this case.

In order to detect positions in the direction of width of a print(hereinafter referred to as "a print width direction", when applicable)for addressing, a self-running IS camera (such as a CCD camera or a MOScamera) is employed, and its output signal is utilized.

The scanning operation of the IS camera 1 is controlled by an externalsynchronizing signal as shown in FIG. 5; that is, the line scanning isrepeatedly carried out at predetermined scanning intervals only when theexternal synchronizing signal is raised to a logical high level(hereinafter referred to merely as "H" or "1", when applicable). The IScamera 1 provides a signal START at the start of scanning and a signalSCLK in synchronization with the scanning, as shown in FIG. 5.

The scanning direction signal input circuit 6 is to control theabove-described three signals, namely, the external synchronizingsignal, the signal START and the signal SCLK. One example of the circuit6 is as shown in FIG. 6.

In response to the signal MZERO signal from the running position signalinput circuit 5, the scanning direction signal input circuit 6 providesthe external synchronizing signal to start the scanning of the IS camera1 (hereinafter referred to merely as "an IS 1", when applicable). Next,in order to repeat the scanning at the same intervals in the directionof rotation of the printing cylinder CY, the signal MCLK is counted by acounter 27 and is compared with the number of division in the directionof rotation of the printing cylinder CY in a comparator 28, which hasbeen set in a latch circuit 30. When the count value reaches the setvalue, the comparator 28 outputs the external synchronizing signal. Thisis repeatedly carried out during a period of time corresponding to oneinspection picture.

On the other hand, upon start of the scanning of the IS 1, the circuitreceives the signal SCLK and the signal START from the IS 1. The signalSCLK is counted by a counter 32. When the count value reaches the numberof division in the direction of scanning which has been set in a latchcircuit 29, a comparator 31 outputs a signal SEND. Control is so madewith the aid of a D type flip-flop 37 and the signals MZERO and MENDthat the signals SZERO and SEND are produced during the inspectionperiod only.

The inspection surface of the printing cylinder CY is related to thesignals MZERO, MEND, SZERO and SEND as indicated in FIG. 7. Theaforementioned address generating circuit 8 operates to generateaddresses on one inspection picture by the use of the outputs of therunning position signal input circuit 5 and the scanning directionsignal input circuit 6. In other words, by dividing the printingcylinder CY into n parts in the direction of rotation and into m partsin the direction of scan as shown in FIG. 8, the inspection picture isdivided into addresses the number of which is as follows. The circuit 8operates to generate the addresses. One example of the circuit 8 is asshown in FIG. 9. ##EQU1##

First, a counter 50 is cleared by the signal MZERO, to initiateaddressing. Then, in response to the signal SZERO the addresses of thefirst line in the direction of scan are generated with the signal SCLK,and the number thereof is counted by a counter 48. This function iscarried out a D type flip-flop 43, an AND circuit 44, and the counter48.

The number of division in the direction of scan is set in a latchcircuit 46 in advance. By comparison of the set value with the countvalue in a comparator 49, the number of addresses for one scanning lineis determined. The address generated by a counter 50 is applied througha latch circuit 51 and the bus to the relevant circuits. The sameoperation is repeatedly carried out to the n-th line. In the example, aninternal clock signal CLK for loading digital data in synchronizationwith an address and a write signal WR synchronous with an address forwriting the loaded data in the reference data memory 14 and the buffermemory 16 are produced.

In the embodiment, in order to load image data in the apparatus of theinvention which are provided by the photo-electric conversion of the IS1, the A/D converter 2 and the digital interface 7 are employed.

In an ordinary A/D converter, with respect to its input analog signal,its output digital signal is linear. On the other hand, a density valueD employed for man to recognize colors is logarithmic with respect tointensity, being represented by D=log₁₀ (I_(O) /I) (where I_(O) is theintensity at the time of incidence, and I is the intensity aftertransmission) for instance in a transmission density. Accordingly, inpractice, an inspecting apparatus employing the logarithmic values ofsignals obtained through photoelectric conversion is desirable becausethe logarithmic values are closer to the man's sensuous scale.

Accordingly, in the example, the A/D converter 2 is such that, when ananalog input subjected to photo-electric conversion is inputted, adigital signal can be provided in accordance with both a linearcharacteristic (1) and a non-linear characteristic (2) as shown in FIG.10, thus approximating a logarithmic characteristic also. In order tomake the outputting timing of the digital data of the A/D converter 2synchronous with the aforementioned addresses, the signal CLK from theaddress generating circuit 8 is utilized.

In the embodiment, a method of loading digital data, as they are, whichare inputted to the digital interface 7 or a method of loading them withthe image emphasized can be employed. The latter method is intended toemphasize the picture patterns on the surface of a print, thereby toemphasize the presence of defects, and can be practiced by spatialfiltering Laplacian, and its one example is as shown in FIGS. 11 and 12.

In this connection, whether the digital data are used as they are orthey are used after the image emphasis has been made is determined asfollows: Those data have been set up by a latch circuit 53, so that oneof the methods is selected by a signal selector 54 and the data areloaded in the apparatus.

An image emphasizing circuit in FIG. 12 is of the following spatialfiltering: ##EQU2## That is, the density D_(ij) of a picture element isrepresented by using those of four picture elements adjacent thereto.Therefore, D_(ij) =4D_(ij) -(D_(i-1),j +D_(i),j-1 +D_(i),j+1+D_(i+1),j).

If, in this connection, nothing is limited, for instance, byarrangement, design, etc., then instead of four picture elements eightpicture elements can be utilized. It goes without saying that the lattermethod provides better results.

In FIG. 12, shift registers 55 and 56 and latch circuits 57 through 65are employed in order to obtain the data of necessary addresses, and inorder to satisfy the above-described formula adders 66, 67, 68, 71 and73, a shift register 69, inverters 70 and 74 and an EXCLUSIVE OR circuit72 are employed. In the embodiment, the data are shifted with the aid ofthe signal CLK so as to be synchronous with the addresses generated bythe address generating circuit 8.

The above-described data inputting system and the relevant signals canbe summarized as shown in FIG. 13.

In the embodiment, all the system is controlled by the computer 21. Inthis connection, the inspecting apparatus of the invention has fourfunctions according to the following modes:

(i) Set mode

(ii) Reference mode

(iii) Inspection mode

(iv) Stop mode

These modes can be changed by a control command signal.

First, in the set mode, set values are provided in the various circuitsby the computer 21. For this purpose, the circuits have commoncomponents so as to receive data from the computer 21 as shown in FIG.14. In FIG. 14, a value peculiar to the respective circuit is set in thedip switch 79.

In order to set a set value in one of the circuits, an address CAddress2for selecting the circuit should coincide with the dip switch 79. Inaddition, the signal of a decoder 77 for decoding the command signal toallow the respective circuit to recognize the set mode and a signalCAddress1 which specifies a particular latch circuit (75 for instance)for setting data in the circuit are used to determine the final data setposition. Data CDATA is written in the latch circuit 75 thus specified,with the aid of the signal CWR from the computer 21. As is clear fromthe above description, in the embodiment, the set values can be readilyprovided and changed by the computer 21.

When a satisfactory print is obtained by the printing operation, themode is switched over to the reference mode (ii). As a result, data forone image which are inputted by the digital interface 7 are written inthe reference data memory 14 by the use of the write signal WR and theaddress from the address generating circuit 8. For the next image, themode of the inspecting apparatus is automatically changed into theinspection mode (iii). The data are compared, in real time, with thedata which have been loaded in the reference mode.

For this purpose, the first, second and third feature extractioncomparison decision circuits 9, 10 and 11 are provided. The stop mode(iv) is used to stop the functions of the inspecting apparatus.

The first feature extraction comparison decision circuit 9 carries outthe comparison and decision of a reference data SD and an inspectiondata ID with the same address for every picture elements. In otherwords, the circuit 9 operates to extract, as an unsatisfactory pictureelement, a picture element which is defined by the following expression:

    |SDij-IDij|>Decision level

where SDij is the data which is read out of the reference data memory14, and IDij is the data which can be inputted through the digitalinterface 7 in real time, as shown in FIG. 15.

One example of the circuit 9 is as shown in FIG. 16. The data SD readout of the reference data memory 14 and the data ID inputted through thedigital interface 7 are supplied to latch circuits 82 and 83,respectively, and are processed by adders 84 and 86, an EXCLUSIVE ORcircuit 85 and an inverter 91, as a result of which the absolute valueof the difference between the data SD and ID is written in a latchcircuit 88. Thereafter, in a comparator 90, the output of the latchcircuit 88 is compared with a decision level data CD1 which is read outof the picture control data memory 15 and set in a latch circuit 89 insynchronization with the above-described data. The result of comparisonis outputted, as a decision result J1, by a D type flip-flop 87 pictureelement by picture element.

In the second feature extraction comparison decision circuit 10, asshown in FIG. 17, the absolute value of the difference between the sumof reference data for one image and the sum of inspection data for oneimage is obtained and compared with the decision level. In other words,the circuit 10 operates to perform the comparison of the following:##EQU3## where n is the number of division, in the direction ofrotation, of the printing cylinder CY, m is the number of division, inthe direction of scan, of the IS 1, SDij is the reference data, and IDijis the inspection data.

Accordingly, the accuracy of detecting low density defects scatteredover the entire image or moderate density variations is improved.

One example of the circuit 10 is as shown in FIG. 18. The data SD readout of the reference data memory 14 are added by means of latch circuits94 and 95, an adder 98 and an AND circuit 92 for one image, and theresult of addition is written in a latch circuit 102 with the aid of theMEND signal. The inspection data loaded through the digitial interface 7are similarly processed by means of latch circuits 96 and 97, an adder99 and an AND circuit 93. In the case of the data ID, the result ofaddition is written in a latch circuit 103 through an inverter 105 forconversion into the complement of one because the difference betweenboth is required. In order to clear the addition data, a signal "0" isinputted to the latch circuits 94 and 96 through the AND circuits 92 and93 once an image. For this purpose, the signal "0" is provided by a Dtype flip-flop 100 with the aid of the signal MEND and the signal MZEROonce an image.

The sum of the reference data thus processed for all the pictureelements and the sum of the inspection data thus processed for all thepicture elements are applied to one input A of a comparator 110 througha circuit for obtaining the absolute value of a difference whichcomprises adders 106 and 108, an EXCLUSIVE OR circuit 107 and aninverter 109. The input is compared with a decision level data CD2 readout of the picture element control data memory 15. When the input ishigher than the decision level, it is outputted as a decision signal J2by a D type flip-flop 112 once an image.

In the third feature extraction comparison decision circuit, as shown inFIG. 19, the absolute value of the difference between the sum of thereference data SD in the direction of run of the print P, i.e., in thedirection of rotation of the printing cylinder CY and the sum of theinspection data in the same direction is obtained and compared with thedecision level. In other words, the circuit 11 carries out thecomparison of the following: ##EQU4## where SDij is the reference data,and IDij is the inspection data.

With the circuit 11, the accuracy of detecting defects (such as doctorstripes) in the direction of rotation which occur frequently withgravure prints.

One example of the circuit 11 is as shown in FIG. 20. The data SD readout of the referene data memory 14 are processed by an AND circuit 120,an adder 121, a memory 127 and a transceiver 129, so that the sum##EQU5## in the direction of rotation at each division point in thedirection of scan is calculated. The content of the memory 127 isrenewed to data added scanning line by scanning line, and finally todata for one image which are added in the direction of rotation. On theother hand, the inspection data ID obtained through the digitalinterface 7 are similarly processed by means of an AND circuit 122, anadder 123, a memory 131 and a transceiver 133. In order to access thememories 127, 128, 131 and 132, a D type flip-flop 113 and a counter 114are employed to generate addresses for every scanning line. In order toprocess the result of addition in the direction of rotation, duringaddition of one line of the next inspection picture the data of thepreceding inspection picture are written in the memories 128 and 132through the transceivers 130 and 134, and the preceding picture isdetermined for acceptability with the timing of the second line orafter.

With the circuit 11, the real time processing can be performedcontinuously.

In order to provide the above-described timing, a D type flip-flop 118,an OR circuit 119 and the signals SEND, MEND and CLK are employed. Theinspection data ID is written in the memory 132 after being convertedinto the complement of one by an inverter 140, because it is necessaryto obtain the difference between the data ID and the reference data SDlater.

The absolute value of the difference between the sum ##EQU6## in thedirection of rotation at the scanning division points and thecorresponding sum ##EQU7## is calculated by a circuit which comprisesadders 135 and 137, an EXCLUSIVE OR circuit 136 and an inverter 139. Theoutput of the circuit is applied to a comparator 138, where it iscompared with a decision level data CD3 which is read out of the pictureelement control data memory 15. When the output is higher than thedecision level, it is outputted as a decision signal J3 by a D typeflip-flop 125.

In the general decision circuit 12, the results provided through thecomparison and decision of the first, second and third featureextraction comparison decision circuits 9, 10 and 11 are generallyjudged as one detected picture, so that they are outputted as signalsfor operating a marker, alarm unit or peripheral output units.

The circuit determines that the detected picture is unsatisfactory onlywhen the defect signal of the first feature extraction comparisondecision circuit 9 occurs the number of times more than a certaindecision level. Thus, in the inspecting apparatus, depending on therequired contents of inspection the decision level for unsatisfactoryprints can be changed.

On the other hand, the defect outputs of the second and third featureextraction comparison decision circuits 10 and 11 mean serious defects.Therefore, even if only one defect output is provided for the detectedpicture, the entire picture is determined unsatisfactory.

One example of the general decision circuit is as shown in FIG. 21. Asthe decision output J1 of the first feature comparison decision circuit9 is applied to the gate of the counter 142, the number of pictureelements, i.e., the number of signals CLK is counted only when thedefect signal is provided. In a comparator 146, the number of defects inone picture is compared to a decision level set in a latch circuit 145.When the former exceeds the latter, then the detected picture isdetermined unsatisfactory, and the signal MEND is applied to a D typeflip-flop 147 to set the latter.

The decision outputs J2 and J3 of the second and third featureextraction comparison decision circuits 10 and 11 are applied to D typeflip-flop 143 and 144 as they are. Therefore, immediately when a defectsignal is produced for the inspected picture, the D type flip-flops 143and 144 are set. Depending on the presence or absence of theabove-described three signals, a detected-picture general decisionsignal TJ is outputted through an OR circuit 148.

Accordingly, prints which are moved at high speed during printing can beinspected with high accuracy and in real time by monitoring the generaldecision signal TJ from the general decision circuit 12.

Now, the picture pattern position detector 3, the picture patternposition signal input circuit 4 and the reference data memory rewritesignal generating circuit 13 will be described.

As was described before, the inspecting apparatus of the invention isapplied mainly to a rotary press.

The position of a picture pattern, which is formed successively on aprint by such a rotary press, is not always constant in a directionperpendicular to the direction of run of the print, i.e., in the printwidth direction. In other words, when prints are supplied to amulti-color rotary press, they are shifted considerably in the widthwisedirection. Therefore, in such a case, the operator moves the printingcylinder of the press in the widthwise direction to adjust the printingposition, or the printing position is automatically adjusted. Thus, evenif a printing operation is normal to provide a correct picture pattern,the position of the picture pattern is not always the same in thewidthwise direction of the print.

The inspecting apparatus of the invention employs a system thatinspection data are compared with reference data read out of thereference data memory 14 to determine the acceptability of prints.Therefore, if the position of a picture pattern on a print P when thedata are written in the reference data memory 14 is shifted in thewidthwise direction from that of the picture pattern on the print P whenthe inspection data are read, these data do not coincide with each otheralthough the picture pattern is satisfactory; i.e., the operationbecomes erroneous.

This will be described with reference to FIGS. 22 and 23 in more detail.

In FIG. 22, reference character ISC designates the image pickup unit ofan image sensor which is included in the IS 1 (FIG. 3), the image pickupunit comprising, for instance, 512 photo-electric conversion elementsarranged linearly in the widthwise direction of the print P; and athrough d, picture patterns which are successively printed on thesurface of the print P.

As was described above, the positions of these picture patterns areshifted in the direction x of the print P, i.e., in the widthwisedirection of the print P, from one another.

In FIG. 23, reference character ISC' designates one of thephoto-electric conversion elements forming the photoelectric converterISC; and a' and b', one of the picture elements of the picture pattern aand one of the picture elements of the picture pattern b, respectively.

It is assumed that, with the picture pattern a in FIG. 22, the data iswritten in the reference data memory 14, and thereafter the data of thepicture pattern b is read out. Furthermore, it is assumed that, as aresult, the positional relation between the picture element a' of thepicture pattern a and the photoelectric conversion element ISC' is asshown in the part (1) of FIG. 23, and the positional relation betweenthe picture element b' of the picture pattern b and the photoelectricconversion element ISC' is as shown in the part (2) of FIG. 23.

In this case, the density data written in the corresponding address inthe reference data memory 14 corresponds to the area a" in the part (3)of FIG. 23, and the inspection data corresponds to the area b" in thepart (4) of FIG. 23.

Accordingly, although the picture patterns a and b are the same, thedata read out of the reference data memory 14 does not coincide with theinspection data; that is, in spite of the correct picture pattern, theprint is determined unacceptable.

In order to overcome this difficulty, the reference data memory rewritesignal generating circuit 13 is provided. The circuit 13 receives apicture pattern position signal from the picture pattern positiondetector 3 and holds picture pattern position data provided when dataare written in the reference data memory 14. Thereafter, in the circuit13, the picture pattern position data is compared with that which isreceived whenever inspection data are read, and when the differencebetween the two data is larger than a predetermined value, a referencedata memory rewrite signal is produced. For this purpose, the picturepattern position detector 3 has an image sensor, so that the position,in the widthwise direction, of a picture pattern printed on the surfaceof a print P is detected, and a picture pattern position signal isapplied through the picture pattern position signal input circuit 4 tothe bus.

One example of a method of detecting a picture pattern position with thepicture pattern position detector 3 is as shown in FIG. 24.

In FIG. 24, reference character a designates a picture pattern printedon a print P; and 3', a detection region by the picture pattern positiondetector 3.

The picture pattern position detector 3 picks up the image of apredetermined region, in the direction x, of the picture-pattern-printedsurface of the print P which is continuously moved in the direction y,and, with the aid of the rotary encoder RE, produces a detection signalwhen the predetermined region comes in the detection region. Therefore,where the position of the picture pattern a on the print P is shifted inthe widthwise direction, or in the direction x, the size of the part ofthe picture pattern a which is covered by the detection region 3' ischanged, and accordingly the amount of light incident to the picturepattern position detector 3 is changed.

Accordingly, the position, in the direction x, of the picture pattern acan be detected by detecting the amount of light applied to the picturepattern position detector 3. Therefore, the light quantity detectionsignal of the detector 3 is employed as a picture pattern positionsignal which is supplied through the picture pattern position signalinput circuit 4 to the bus.

FIG. 25 shows another example of the method of detecting a picturepattern position. In FIG. 25, reference character M designates awedge-shaped registering mark. In the case of a multi-color rotarypress, for automatic registration in the print width direction, thewedge-shaped registering mark is provided in the margin of a print. Inthe example, the image of the registering mark M is picked up by thepicture pattern position detector 3, and as shown in the parts (a) and(b) of FIG. 25 the variation of the area of the registering mark M whichis included in the detection region is detected as a variation in thequantity of light from the picture pattern position variation Δx in thewidthwise direction, to provide the picture pattern position signal.

Therefore, according to the example, the detecting operation can becarried out more positively because a mark suitable for positiondetection can be employed irrespective of a picture pattern employed.

FIG. 26 shows another example of the picture pattern position detectingmethod. In FIG. 26, reference numeral N designates a position shiftdetecting mark which is printed on the margin of a print.

The mark N consists of a number of segments which are arranged in thedirection of width (x) of the print and are in parallel with thedirection of run (y). In the method, a picture pattern position signalis provided by the utilization of the fact that, according to a positionvariation Δx in the directon of width, the number of segments covered bythe detecting region 3' changes.

Thus, according to the example, the picture pattern position signal canbe readily obtained as the number of pulses.

FIG. 27 shows one example of the reference data memory rewrite signalgenerating circuit 13. The circuit 13 is made up of a microcomputer MChaving input/output ports P₁ through P₆, latch circuits 150 through 152,a counter 153 and an AND circuit 154.

FIG. 28 is a flow chart for a description of the operation of thecircuit 13. When the microcomputer MC starts according to the flowchart, the microcomputer MC determine what the content of the controlcommand COMMAND is. When the content is the "stop" or "set" mode,reading the control command COMMAND is repeated. However, in the case ofthe "set" mode, position allowable value data CD is inputted through thelatch circuit 150 to the port P₂ of the microcomputer MC.

When the content of the control command COMMAND is the "reference" mode,the picture pattern position data PD is inputted through the latchcircuit 152 to the port P₆ of the microcomputer MC, and is stored as thereference position data of the picture pattern provided when thereference value data is read. Thereafter, the control command COMMAND isread.

When the content of the control command COMMAND is the "inspection"mode, the operation is as follows:

(1) The position allowable value data CD4, which is inputted to the portP₂ in the "set" mode, is transferred to a register in the microcomputerMC;

(2) Similarly as in the "reference" mode, the picture pattern positiondata PD is received. The data thus received is compared, as the positiondata in receiving the detection value data, with the reference positiondata, to calculate the absolute value of the difference therebetween;

(3) The absolute value of the difference is compared with the positionallowable value data CD4. When the former is larger than the latter, areference data memory rewrite signal is generated; and

(4) Reading the control command COMMAND is carried out again.

Thus, according to this example, when the position shift, in thedirection of width, of the picture pattern on the print P becomes largerthan a preset value, the reference value memory rewrite signalgenerating circuit 13 supplies the rewrite signal RWR to the referencedata memory 14. Thereupon, the image data, which is read by the IS 1, iswritten, as a new reference data, in the reference data memory 14. Theinspection data are determined according to the new reference data untilthe rewrite signal RWR is generated again. Therefore, even if theprinted picture pattern is shifted in the direction of width which isperpendicular to the direction of run of the print, no erroneousoperation is made, and it can be determined correctly whether or not thepicture pattern is acceptable.

Now, the function which is performed by the latch circuit 151, thecounter 153 and the AND circuit 154 in the reference data memory rewritesignal generating circuit 13 will be described.

As was described before, with the inspecting apparatus of the invention,the print P run at high speed is scanned by the IS 1 made up of theone-dimensional line sensors in the direction x perpendicular to thedirection of run y as shown in FIG. 29, so that the image data is read.Therefore, the image data is actually read by the IS 1 in a direction Awhich is obtained by combining the direction of run (y) of the print Pand the direction of scan (x) of the IS 1.

Accordingly, as the speed of run of the print P changes, the image datareading direction A is also changed from that shown in the part (a) ofFIG. 30 to that shown in the part (b) of FIG. 30, for instance. In otherwords, if, even under the condition that the speed of scan of the IS 1is maintained constant, the speed of run of the print changes, then thedirection of read (A) by the IS 1 is changed into that (B).

Let us consider the same picture element detecting regions C and D ofthe IS 1 in the parts (a) and (b) of FIG. 30. In the part (a), theregion reads black picture pattern data. On the other hand, in the part(c), white picture pattern data are partly included in the detectingregion. Thus, although the same picture pattern has been read, thepicture element data of the corresponding addresses differ from eachother.

Accordingly, if the speed of run of the print P in setting the referencedata is different from that in reading the inspection data, then theresult of inspection will be erroneous.

In order to eliminate this difficulty, the speed allowable value data CD5 is supplied to the latch circuit 151, the signal MCLK supplied to thebus through the running position signal input circuit 5 by the rotaryencoder RE is inputted to the AND circuit 154, and when the differencebetween the speed of run of the print P in setting the reference dataand the speed of run of the print P in reading the inspection data ismore than the allowable value, the signal RWR is produced. This will bedescribed with reference to a flow chart shown in FIG. 31.

When the signal is supplied to the circuit 13 through the bus, themicrocomputer MC reads the content of the control command COMMAND. Whenthe content is the "stop" or "set" mode, reading the control commandCOMMAND is repeated. However, in the case of the "set" mode, the speedallowable value data CD5 is written in the port P₅ of the microcomputerMC through the latch circuit 151.

In the case where the content of the control command COMMAND is the"reference" mode, the operation is as follows:

(1) After the counter 153 is reset by a signal outputted by themicrocomputer MC, a count start signal is applied to the AND circuit154, and the pulse MCLK from the rotary encoder RE is received;

(2) The microcomputer MC counts a predetermined period of time;

(3) The microcomputer MC supplies a count finish signal to the counter153, and receiving the pulse MCLK from the rotary encoder RE isfinished;

(4) The count value of the counter 153 is inputted through the port P₃to the microcomputer MC, and is stored, as the running speed data inreceiving the reference value data, in the register in the microcomputerMC; and

(5) Reading the control command COMMAND is effected again.

In the case where the content of the control command COMMAND is the"inspection" mode, the operation is as follows:

(1) The speed allowable value data, which is inputted to the port P₅ inthe "set" mode, is transferred to the register in the microcomputer MC;

(2) Similarly as in the "reference" mode, the pulse MCLK from the rotaryencoder RE is received;

(3) The absolute value of the difference between the running speed datain receiving the inspection value data and that in receiving thereference value data is obtained;

(4) When the absolute value of the difference is more than apredetermined value in view of the speed allowable value, the referencevalue memory rewrite signal RWR is outputted to the bus; and

(5) Reading the control command COMMAND is carried out again.

As was described above, in the embodiment, the speed data, in receivingthe inspection value data, of a print under inspection is compared withthe speed data in receiving the reference value data which has beenstored in advance, and when the difference exceeds the predeterminedvalue, the reference value data is rewritten. Therefore, the erroneousdecision of prints under inspection, which attributes to the differencein running speed, can be prevented according to the invention.

Another embodiment of the invention using the picture element controldata memory 15 will described.

In a rotary press to which the technical concept of the invention isapplicable, prints P are not always constant in width; that is,frequently printing is made by using printing sheets different in width.In this case, it is desirable that the width of the inspection region ischanged. More specifically, it is desirable that, when a print's width Ais changed to one B as shown in FIG. 32, the portions C are masked.

In such an inspecting method, the relation between print picture patterndensities and detected intensities are logarithmic as indicated in FIG.33. Therefore, if the decision level in comparison of reference data anddetection data is fixed as shown in FIG. 33, then in the low densityrange the absolute difference between the detected intensity and thedecision level is insufficient, and accordingly it is impossible todetermine whether or not the picture pattern is acceptable. Accordingly,it is desirable that the decision level is changed as a function of thereference data (by multiplying the latter by a ratio (0 through 1) forinstance 10%).

Furthermore, it is preferable that portions B of one picture A aremasked as shown in FIG. 35, and that the decision level is changedaccording to a portion D (such as a margin) of a picture pattern C forwhich no inspection is required, a portion E for which ordinaryinspection should be performed and a portion F which should be inspectedespecially strictly. That is, it is desirable that the decision level isfinely controlled according to the contents of the picture pattern of aprint under inspection.

In the following embodiment, masking and changing the decision level arecarried out by the same means. Desired portion of the picture patternare selectively masked, and decision levels different according to thecontents of a picture pattern are set up as desired. In order that thearrangement is simplified and the inspection is performed withoutlowering the yielding of prints with the picture pattern beingmaintained high in quality, the picture element control data memoryhaving addresses corresponding to those in the reference data memory isprovided, and in the inspecting operation by comparison of inspectiondata with reference data the decision level is set for each pictureelement according to the data which are read out of the picture elementcontrol data memory.

Similarly as in the case of the reference data memory 14 described withreference to FIG. 2, the picture element control data memory 15 has thesame memory contents as the reference data memory 14 as shown in FIG.37. Furthermore, similarly the memory 15 is so designed that controldata corresponding to the addresses a in the reference data memory 14are written in and read out of the addresses a' which are arranged inthe direction of width of a print and in the direction of run.

FIG. 38 shows one example of the first feature extraction comparisondecision circuit 9 in the embodiment. When the inspection is startedafter the printing operation has been started, the inspection data ID,and the data SD and the data CD1 from the reference data memory 14 andthe picture element control data memory 15 are successively read for thesame addresses and are loaded in latch circuits 220 through 223.

The reference data SD in positive state which is applied to the latchcircuit 222 and the detection data ID in negative state which is appliedto the latch circuit 223 are processed by a circuit comprising anaddition circuit 229, an inverter 230, an EXCLUSIVE OR gate 231 and anaddition circuit 232, as a result of which data D_(D) representing theabsolute value of the difference between the inspection data ID and thereference data SD is provided and is then written in a latch circuit225, i.e., D_(D) =|ID-SD| is obtained. The data D_(D) is applied to oneinput B of a comparator 223 by the latch circuit 225.

The reference data SD from the latch 221 is applied to a shift register227, where it is shifted as much as a predetermined number of bits. As aresult, the data SD is multiplied by a predetermined coefficient K(smaller than one); that is, data KSD is applied to one input B of aselection circuit 228.

On the other hand, the control data CD1, which has been loaded in thelatch circuit 220, is read out as it is and is applied to the otherinput B of the selection circuit 228. The control data CD1 is furtherapplied through an OR gate 226 to the selection input S of the selectioncircuit 228. The selection circuit 228 operates to output the dataapplied to the input B when the selection input S is at the "H" leveland the data applied to the input A when the selection input S is at the"L" level.

In the comparator 223, data JL at the input A is compared with the dataD_(D) at the input B. Only when the data D_(D) at the input B is largerthan the data at the input A, the comparator produces an "H" leveloutput J. That is, the comparison is carried out with the data JL as adecision level, to provide the output J.

Accordingly, the computer 21 monitors the output J of the comparator233. More specifically, the computer 21 determines that, when the outputJ is at the "L" level, the picture pattern portion corresponding to theaddress of the memories 14 and 15 has no defect, and determines that,when the output J is at the "H" level, it has a defect, to perform thepredetermined operation.

It is assumed that the control data written in an address in the picturecontrol data memory 15 is (O,O)_(H) ; i.e., all eight bits are "O".

When the inspection data of the picture pattern portion corresponding tothe address is read out and the inspection is going to be performed, theoutput of the OR gate 226 is set to the "L" level, and therefore theselection circuit 228 writes the data KSD at the input A in the latchcircuit 224.

As a result, the data JL representing the decision level of thecomparator 233 is the data KSD which is obtained by shifting thereference data SD in the shift register 227, i.e., by multiplying thedata SD by the coefficient K. With the data KSD, it is determinedwhether or not the picture pattern is acceptable. In this case, thepicture pattern is inspected according to the system in which thedecision level changes as the function of the reference data asdescribed with reference to FIG. 34.

Accordingly, if the data (O,O)_(H) is written in an optional address inthe picture element control data memory 15, then the picture patternportion corresponding to the address is inspected according to thesystem in which the decision level changes as the function of thereference data. In this connection, it goes without saying that theaddressing may be effected for each group of picture elements instead ofeach picture element.

It is assumed that the control data written in an address in the pictureelement control data memory 15 is other than (O,O)_(H) ; i.e., at leastone of the eight bits is "1".

In this case, the output of the OR gate 226 is raised to the "H" levelwhen the inspection data of a picture pattern portion corresponding tothis address is read out. Therefore, the selection circuit 228 suppliesthe data CD1 at its input B to the latch circuit 224, as it is.

Accordingly, in this case, the comparator 223 operates with the controldata CD1 read out of the address as the decision level. Therefore, withthe control data written in the picture element control data memory 15,different decision levels can be provided for different addresses of apicture pattern in the inspection thereof.

For instance, as shown in FIG. 36, a picture pattern C on a print to beinspection has a portion D such as a margin for which no inspection isrequired. For such a portion D, the control data to be written in theaddress is made sufficiently large, whereby the decision level is sethigh for the portion and the presence or absence of slight defects isneglected. For an essential portion E, the control data to be written inthe address is made small and the decision level is set low, so that theportion E is strictly inspected. For a more essential portion F, thedecision level is set lower. Thus, control is performed finely for theprovision of satisfactory prints.

If, in this connection, the control data (F,F)_(H) is written in theaddress in the picture element control data memory 15 which correspondsto the portion B in FIG. 35 or the portion D in FIG. 36, then for thisportion the output J of the comparator 233 is set to "L" at all timesirrespective of the data D_(D). Therefore, the same result as that inthe case where no inspection is carried out for picture pattern defectsis obtained; that is, masking operation is effected for optional picturepattern portions.

A control data writing method for the picture element control datamemory 15 will be described.

As is apparent from FIG. 3, in the embodiment, all the operations arecontrolled by the computer 21, and writing control data in the pictureelement control data memory 15 is also controlled by the computer 21.

The writing operation will be concretely described.

(1) When an optional value is set, as a decision level, in the pictureelement control data memory 15:

As shown in FIG. 39, decision level data having optional values aresuccessively applied to the picture element control data memory 15, soas to be written and set therein.

(2) When data obtained by multiplying the reference data by a ratio K(K<1) is set, as a decision level, in the picture element control datamemory 15:

As shown in FIG. 40, the content of the reference data memory 14 isloaded through the computer interface 17 into the CPU of the computer21. Thereafter, in the CPU, the content is multiplied by a ratio K (K<1)for every picture element of the reference data, to obtain datarepresenting a decision level. In this case, in a low density levelregion (small in digital value) multiplication of the ratio K may resultin "O". Therefore, a minimum value which can be set should bepredetermined, or a certain value should be added to the product of thereference data and the ratio K.

The data thus provided to represent decision levels for the pictureelements are set in the picture element control data memory 15 throughthe computer interface 17. It goes without saying that a hardwarearrangement may be employed for setting such data.

(3) When the reference data is monitored, and the position of anoptional portion of the picture pattern is determined with a cursor orthe like, so that a decision level is set in the picture element controldata memory 15 for every optional portion:

As shown in FIG. 40, the content of the reference data memory 14 isloaded into the CPU through the computer interface 17 and inputted tothe CRT, so that it can be monitored as an image. A portion of thepicture pattern reproduced is specified by moving the cursor and theposition of the portion is loaded into the CPU, so that an optionaldecision level at that position is set in the picture element controldata memory 15 through the computer interface 17 by the CPU.

(4) When the contour portion of a picture pattern is extracted out ofthe reference data, and a special decision level provided for thatportion is set in the control data memory:

As shown in FIG. 40, the content of the reference data memory 14 isloaded through the computer interface 17 into the CPU, and a digitalimage processing operation is carried out in order to extract thepicture pattern contour portion out of the data. An optional decisionlevel is determined for the address of the contour portion thusextracted, and the data is set in the picture element control datamemory 15 through the computer interface 17.

A method of extracting components representing a contour portion in alongitudinal or lateral direction out of the picture pattern of suchimage data is according to a spatial filtering technique which isgenerally employed in digital image processing. By this method, theobject can be readily achieved.

If the densities of points in a 3×3 square region with an optional pointfij of a picture pattern as the center are employed, a spatial filterused for extracting a contour in the longitudinal direction is: ##EQU8##and a spatial filter used for extracting a contour in the lateraldirection is: ##EQU9##

In the case where the contour of a picture pattern is merely obtained,the spatial filter in a method of obtaining differences in fourdirections according to the Laplacian process is: ##EQU10## and thespatial filter in a method of obtaining differences in eight directionsis: ##EQU11##

In the case of paragraph (4), the contour portion of a picture patternis extracted and the special decision level is provided. This is due tothe following reason: For the portion of a picture pattern, in which thedensity changes abruptly, the detecting operation is greatly affected bythe position shift which may occur in detecting defects. That is,because of the position shift the detecting operation is carried out asif defects were involved, although no defects are included; i.e., thedetection is liable to become erroneous. In order to overcome thisdifficulty, the contour portion of the picture pattern is detected, andthe decision level for this portion only is made higher than those forother portions. In this case, the possibility of erroneous operation dueto the position shift can be reduced without increasing the decisionlevel as a whole so much.

In the inspection as described above, in order to detect defects such asdoctor stripes in the direction of rotation which may occur in gravureprinting, the longitudinal length of one picture element detection areashould be larger than the lateral length as shown in the parts (A) and(B) of FIG. 41. Even when, in this case, the position is shifted by thesame distance (ΔX or ΔY), one picture element photoelectric elementdetection area is affected more greatly by the position shift in thelateral direction X than by the position shift in the longitudinaldirection Y, as is apparent from the parts (A) and (B) of FIG. 42.

Accordingly, if the above-described method, in which the contour portionis detected, and for the portion the decision level in the lateraldirection is made higher than the decision level in the longitudinaldirection, is employed, the frequency of erroneous operation due to theposition shift is reduced, and the possibility of increasing thefrequency of erroneous operation can be eliminated without lowering thedefect detecting accuracy as a whole.

It is unnecessary to individually conduct the control data settingoperations described in paragraphs (1) through (4) above. That is, theymay be conducted in association with other setting methods in softwareand hardware senses, by taking the reduction of data setting time andthe manufacture of hardware into consideration.

One example of the data setting method in such a case is as indicated bya flow chart in FIG. 43.

In the block diagram of FIG. 3, the buffer memory 16 is provided fortransmitting and receiving the data which are necessary for theoperation of the computer 21, and the monitoring address generatingcircuit 18 and the monitor interface 19 are provided for applying theinternal digital data to the monitor 20. The computer 21 is, forinstance, a personal computer. It goes without saying that the computer21 is provided to control all the operations of the inspectingapparatus.

In the above-described embodiment, the inspecting position is on theprinting cylinder; however, it goes without saying that the technicalconcept of the invention is applicable to off-line inspection andsheet-prints inspection, if the arrangement is so modified as to detectthe absolute position of the picture pattern.

INDUSTRIAL APPLICABILITY

As was described above, according to the invention, the apparatus can beprovided which, even when prints are run at considerably high speed asin the case of a rotary press, can inspect the prints in real time andwith high accuracy.

Accordingly, only the prints which are satisfactory in finish can bepicked up, while the prints which are unsatisfactory can be positivelydiscarded.

What is claimed is:
 1. A method of inspecting prints comprising thesteps of:writing reference data from a reference print in a referencedata memory; comparing image data obtained from a running print underinspection with said reference data for every printing element; anddetermining whether or not said print is acceptable through saidcomparison of two data; characterized by: loading print running speeddata while loading said reference data; comparing said print runningspeed data loaded during loading said reference data with print speeddata loaded during said image data obtained from a print underinspection; and rewriting said reference data when the differencebetween said two speed data exceeds a predetermined value.
 2. A methodaccording to claim 1 wherein said method further comprises the stepsof:reducing an image of said reference data read out of said referencedata memory; specifying an optional portion of said image; and enablingto write data in the corresponding address in a control data memory. 3.A method as claimed in claim 1, wherein said method further comprisesthe steps of:recognizing said control data read out of said control datamemory; arithmetic processing said reference data read out of saidreference data memory; and selecting said decision level in comparisonof said inspection data with said reference data by switching outputdata obtained by said arithmetic processing and said control data readout of said control data memory.
 4. A method as claimed in claim 1,wherein said method further comprises the steps of:determining the levelof control data read out of said control data memory; and setting thedecision level in the comparison of said detection data with referencedata to a sufficiently high value when the level of said control data ishigher than a predetermined value.
 5. A method as claimed in claim 1,wherein said method further comprises the steps of:reproducing an imageof said reference data read out of said reference data memory;specifying an optional portion of said image and; enabling to write datain the corresponding address in said control data memory.
 6. A methodclaimed in claim 1, wherein said method further comprises the stepsof:extracting the contour portion of an image according to saidreference data read out of said reference data memory; and writing datain the corresponding address in said control data memory.
 7. A printinspecting apparatus of the type that a memory capable of storing imagedata read out of one picture pattern on a running print is provided,image data read out of said memory employed as reference data whileimage data read out of the remaining picture patterns is employed asinspection data, and said reference data and inspection data aresubjected to comparison to determine whether or not said print isacceptable, characterized by comprising:a control data memory havingaddresses which are provided for every printing element of image data;and a data setting means for writing control data for determining anallowable difference of said inspection data with reference to saidreference data in said control data memory for every printing element ofsaid image data, so that a decision for at least one of the referenceand inspection data comparison operations by a first, second and thirdcomparison means is set up according to control data read out of saidcontrol memory; said data setting means comprising: monitor means forreproducing on an image display surface said reference data read out ofsaid reference data memory, and means for specifying an optional portionof said image display surface of said monitor means, so as to write in acorresponding address in said control data memory.